Distribution manifolds for internal combustion engines are well known, especially intake manifolds for distribution of air to the combustion cylinders of an engine. In the older prior art, such manifolds were formed of metal, typically by die casting or “lost mold” casting. Aluminum manifolds are well known and are desirable for being lighter than comparable cast iron manifolds. Aluminum manifolds, however, are excellent transmitters of engine noise and are expensive to manufacture.
In more recent prior art, manifolds are typically formed by injection molding of polymer composites in a plurality of separate sections, followed by joining of the sections by welding such as friction welding. See, for example, U.S. Pat. No. 6,679,215, the relevant disclosure of which is herein incorporated by reference. Exemplary polymer composites for use in forming intake manifolds are glass-filled nylon and glass-filled polyphthalamide. Such polymer composite manifolds transmit much less engine noise, are at least as light as aluminum manifolds, and are less expensive to manufacture.
A drawback of polymer composite manifolds manufactured by prior art methods and apparatus is that the wall thickness is limited to about 4 mm, although thicker walls are desirable in some regions of a manifold to reduce transmission of engine vibration and to raise the harmonic frequency of the walls. In modern tuned manifolds, there is typically a septum between two plenums directed to odd and even numbered cylinders, respectively. This septum is typically a flat planar element susceptible to vibration. Attempts to increase the septum thickness above about 4 mm have created increased process cycle times, and have resulted in increased warpage, increased shrinkage, and unacceptable overall dimensional changes in the molded components.
What is needed in the art is means for increasing the effective thickness of a manifold plenum septum without causing unacceptable dimensional changes.
It is a principal object of the present invention to provide an improved manifold having reduced propensity for vibration and noise transmission.